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Abstract:

Disclosed is an edge type backlight unit having a local dimming function
realized by adjusting the distance between a light guide plate and a
plurality of optical systems disposed under the light guide plate. The
edge type backlight unit includes a light guide plate guiding light
emitted from a light source, and a luminance control unit including a
plurality of optical systems reflecting light guided by the light guide
plate and emitting the light to a liquid crystal panel, and controlling
luminance by controlling the reflectance of each of the plurality of
optical systems according to an input image signal.

Claims:

1. An edge type backlight unit having a local dimming function
comprising:a light guide plate guiding light emitted from a light source;
anda luminance control unit including a plurality of optical systems
reflecting light guided by the light guide plate and emitting the light
to a liquid crystal panel, the luminance control unit controlling
luminance by controlling the reflectance of each of the plurality of
optical systems according to an input image signal.

2. The edge type backlight unit of claim 1, wherein the luminance control
unit further comprises a controller supplying control voltages, each
having a voltage level varied according to the contrast of the image
signal, to the plurality of optical systems, respectively.

3. The edge type backlight unit of claim 2, wherein the optical systems
each have a variable distance from the light guide plate, the distance
being controlled by piezoelectric effects.

4. The edge type backlight unit of claim 2, wherein the luminance control
unit further comprises a plurality of first electrodes disposed under the
light guide plate in one-to-one correspondence with the plurality of
optical systems,wherein the controller applies the control voltages to
the first electrodes and the optical systems, respectively, andthe
optical systems each have a variable distance from the light guide plate,
the distance being controlled by an electrostatic force with the first
electrode.

5. The edge type backlight unit of claim 4, wherein the luminance control
unit further comprises a plurality of second electrodes disposed under
the light guide plate in one-to-one correspondence with the plurality of
optical systems,wherein the controller applies the control voltages to
the first electrodes, the optical systems and the second electrodes
respectively, andthe optical systems are disposed between the first
electrodes and the second electrodes, and each have a variable distance
from the light guide plate, the distance being controlled by an
electrostatic force with the first and second electrodes.

6. The edge type backlight unit of claim 2, wherein the luminance control
unit further comprises a spacer spacing the optical system from the light
guide plate at a preset distance.

7. The edge type backlight unit of claim 1, wherein the optical system is
one of a reflection plate reflecting light, a scattering pattern
scattering light, and a diffusion sheet diffusing light.

8. The edge type backlight unit of claim 7, wherein the optical system
includes a coating layer increasing light reflectance, on a surface
thereof.

9. The edge type backlight unit of claim 4, wherein the first electrode is
formed of a transparent material.

10. The edge type backlight unit of claim 5, wherein the first electrode
or the second electrode is formed of a transparent material.

11. The edge type backlight unit of claim 1, further comprising an optical
member directing light, emitted from the light source to the light guide
plate, to a preset direction.

12. The edge type backlight unit of claim 1, wherein the light source
controls the quantity of incident light in association with the luminance
control of the luminance control unit.

13. The edge type backlight unit of claim 4, wherein the luminance control
unit further comprises a spacer spacing the optical system from the light
guide plate at a preset distance.

14. The edge type backlight unit of claim 5, wherein the luminance control
unit further comprises a spacer spacing the optical system from the light
guide plate at a preset distance.

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001]This application claims the priority of Korean Patent Application
No. 10-2008-0119938 filed on Nov. 28, 2008, in the Korean Intellectual
Property Office, the disclosure of which is incorporated herein by
reference.

BACKGROUND OF THE INVENTION

[0002]1. Field of the Invention

[0003]The present invention relates to an edge type backlight unit, and
more particularly, to an edge type backlight unit, which is capable of
local dimming through the adjustment of the distance between a light
guide plate and a plurality of optical systems disposed under the light
guide plate.

[0004]2. Description of the Related Art

[0005]With the increasing use of information apparatuses, slim and
lightweight flat panel display devices using small amounts of power have
recently drawn much attention.

[0006]Among those flat panel display devices, liquid crystal displays
(LCDs) are being widely used for notebook computers, desktop monitors,
and televisions because of their excellent resolution, color display and
image quality.

[0008]In LCDs, the backlight unit is installed under the liquid crystal
panel to emit light to the liquid crystal panel. The LCD displays an
image by controlling the amount of light according to the alignment of
liquid crystals, thereby displaying an image.

[0009]Backlight units may be grouped into a direct type and an edge type.
Direct type backlight units include light sources under the liquid
crystal panel to emit light directly onto the entire surface of a
substrate. Edge type backlight units include light sources disposed at
one or both edges of a light guide plate to reflect the light emitted
from the light sources toward the liquid crystal panel.

[0010]LCDs are being widely used to display moving pictures such as movies
and dramas, and require a local dimming function for the vivid expression
of images with varying luminance.

[0011]To realize local dimming, direct type backlight units, directly
emitting light to the bottom of the liquid crystal panel, may employ
light emitting diodes (LEDs) as light sources. However, the LEDs need to
be spaced apart from the liquid crystal panel at a predetermined interval
in order to achieve uniform luminance, adversely affecting the tendency
toward slim and lightweight displays.

[0012]In contrast, edge type backlight units use less space because light
falling upon the edges is reflected by light guide panels, which are
contributive to achieving slim and lightweight displays. However, the
edge type backlight units are unable to perform local dimming because
light falls upon the edges of the light guide plate and is reflected
toward the bottom of the liquid crystal panel.

SUMMARY OF THE INVENTION

[0013]An aspect of the present invention provides an edge type backlight
unit, which can realize local dimming through the adjustment of the
distance between a light guide plate and each of a plurality of optical
systems disposed under the light guide plate.

[0014]According to an aspect of the present invention, there is provided
an edge type backlight unit having a local dimming function, including: a
light guide plate guiding light emitted from a light source; and a
luminance control unit including a plurality of optical systems
reflecting light guided by the light guide plate and emitting the light
to a liquid crystal panel, the luminance control unit controlling
luminance by controlling the reflectance of each of the plurality of
optical systems according to an input image signal.

[0015]The luminance control unit may further include a controller
supplying control voltages, each having a voltage level varied according
to the contrast of the image signal, to the plurality of optical systems,
respectively.

[0016]The optical systems may each have a variable distance from the light
guide plate, the distance being controlled by piezoelectric effects.

[0017]The luminance control unit may further include a plurality of first
electrodes disposed under the light guide plate in one-to-one
correspondence with the plurality of optical systems. The controller may
apply the control voltages to the first electrodes and the optical
systems, respectively, and the optical systems may each have a variable
distance from the light guide plate, the distance being controlled by an
electrostatic force with a corresponding electrode of the first
electrodes.

[0018]The luminance control unit may further include a plurality of second
electrodes disposed under the light guide plate in one-to-one
correspondence with the plurality of optical systems. The controller may
apply the control voltages to the first electrodes, the optical systems
and the second electrodes respectively, and the optical systems may be
disposed between the first electrodes and the second electrodes, and each
have a variable distance from the light guide plate, the distance being
controlled by an electrostatic force with respective corresponding
electrodes of the first and second electrodes.

[0019]The luminance control unit may further include a spacer spacing the
optical system from the light guide plate at a preset distance.

[0020]The optical system may be one of a reflection plate reflecting
light, a scattering pattern scattering light, and a diffusion sheet
diffusing light.

[0021]The optical system may include a coating layer increasing light
reflectance, on a surface thereof.

[0022]The first electrode may be formed of a transparent material.

[0023]The first electrode or the second electrode may be formed of a
transparent material.

[0024]The edge type backlight unit may further include an optical member
directing light, emitted from the light source to the light guide plate,
to a preset direction.

[0025]The light source may control the quantity of incident light in
association with the luminance control of the luminance control unit.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026]The above and other aspects, features and other advantages of the
present invention will be more clearly understood from the following
detailed description taken in conjunction with the accompanying drawings,
in which:

[0027]FIG. 1 is a schematic view of an edge type backlight unit according
to the present invention;

[0028]FIGS. 2A and 2B are views of an edge type backlight unit according
to an exemplary embodiment of the present invention;

[0029]FIGS. 3A and 3B are views of edge type backlight units according to
other exemplary embodiments of the present invention; and

[0030]FIG. 4 is a view illustrating local dimming of an edge type
backlight unit according to an exemplary embodiment of the present
invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0031]Exemplary embodiments of the present invention will now be described
in detail with reference to the accompanying drawings.

[0032]FIG. 1 is a schematic view of an edge type backlight unit according
to the present invention.

[0033]Referring to FIG. 1, the edge type backlight unit 100, according to
the present invention, includes a light guide plate 110 and a luminance
control unit 120.

[0034]The light guide plate 110 is disposed under a liquid crystal panel,
and light from light sources `1` falls onto the edges of the light guide
plate 110. The light guide plate 110 guides the incident light to
illuminate the liquid crystal panel. The light sources `1` may emit light
at one or both edges of the light guide plate 110. Luminance is
controlled according to the amount of light being emitted to the liquid
crystal panel.

[0035]The luminance control unit 120 is disposed under the light guide
plate 110, and includes optical systems reflecting light inside the light
guide plate 110. The luminance control unit 120 controls luminance by
adjusting the reflectance of each of the optical systems. Here, the
luminance is controlled by adjusting the distances between the optical
systems and the light guide plate 110, and the optical systems are
disposed in plurality under the light guide plate 110. By controlling
luminance levels selectively for the coverage area of each of the optical
systems, luminance can be adjusted locally, that is, local dimming can be
performed.

[0036]Hereinafter, edge type backlight units according to embodiments of
the present invention will be described in detail with reference to the
drawings.

[0037]FIGS. 2A and 2B illustrate an edge type backlight unit according to
an exemplary embodiment of the present invention. FIGS. 2A and 2B are
enlarged views of a coverage area of an optical system in the edge type
backlight unit according to this embodiment.

[0038]Referring to FIG. 1 and FIG. 2A, the luminance control unit 120 of
the edge type backlight unit 100, according to the present invention, may
include a controller 121, optical systems 122, and spacers 123.

[0039]The controller 121 transmits control voltages, which have voltage
levels varying with the contrast of an image signal sent from the
outside, to the respective optical systems 122.

[0040]The optical systems 122 may each include any one of a reflector
plate that reflects light diffused to a downward direction of the light
guide plate 110, a scattering pattern that scatters light, and a
diffusion sheet that diffuses light. Furthermore, the optical system 122
may include a coating layer to increase light reflectance properties.

[0041]The optical systems 122 are formed of a piezoelectric body. Thus,
the optical systems 122 each have a variable distance from the light
guide plate 110, which is controlled by piezoelectric effect when
receiving the control voltage, thereby controlling luminance.

[0042]That is, when the optical system 122 moves closer to the bottom of
the light guide plate 110, light is reflected to increase the amount of
light being emitted to the liquid crystal panel, thus increasing
luminance.

[0043]In contrast, as shown in FIG. 2B, as the optical system 122 is
spaced farther apart from the bottom of the light guide plate 110, light
reflection is reduced to decrease the amount of light being emitted to
the liquid crystal panel, thereby decreasing luminance.

[0044]The spacer 123 spaces the light guide plate 110 and the optical
systems 122 apart from each other at a preset distance.

[0045]The luminance control unit 120 employed in the edge type backlight
unit 100 of the present invention may have various embodiments. These
will now be described in detail with reference to the drawings.

[0046]FIGS. 3A and 3B illustrate edge type backlight units according other
embodiments of the present invention. FIGS. 3A and 3B are enlarged views
of the coverage area of one optical system in the edge type backlight
unit illustrated in FIG. 1.

[0047]Referring to FIG. 3A, the luminance control unit employed in an edge
type backlight unit 200, according to another exemplary embodiment of the
present invention, may include a plurality of first electrodes 222a
disposed under a light guide plate 210 in one-to-one correspondence with
a plurality of optical systems 222b. As shown in FIG. 3A, the first
electrodes 222a may be disposed under the optical systems 222b or between
the light guide plate 210 and the optical systems 222b.

[0048]A controller 221 applies control voltages to the optical systems
222b and the first electrodes 222a, respectively. Control voltages of the
same or opposite polarities may be applied to the optical system 222b and
the first electrode 222a.

[0049]That is, in order to increase luminance, control voltages of the
same polarity are applied to the optical system 222b and the first
electrode 222a, so that the optical system 222b can be moved closer
toward the bottom of the light guide plate 210 by the electrostatic force
generated by the electrically charged optical system 222b and first
electrode 222a.

[0050]In contrast, to decrease luminance, control voltages of opposite
polarities are applied to the optical system 222b and the first electrode
222a, so that the optical system 222b can be spaced farther apart from
the bottom of the light guide plate 210 by the electrostatic force
generated by the electrically charged optical system 222b and first
electrode 222a.

[0051]If the first electrode 222a is disposed between the optical system
222b and the light guide plate 210, the controller 221 may apply control
voltages of opposite polarities to the optical system 222b and the first
electrode 222a in order to increase luminance. In this case, the
controller 221 may apply control voltages of the same polarity to the
optical system 222b and the first electrode 222a to decrease luminance.

[0052]FIG. 3B illustrates an edge type backlight unit 300 according to
another exemplary embodiment of the present invention.

[0053]Referring to FIG. 3B, a luminance control unit employed in the edge
type backlight unit 300, according to this embodiment, may further
include a plurality of second electrodes 322c in one-to-one
correspondence with a plurality of optical systems 322b.

[0054]A controller 321 applies control voltages to the optical systems
332b, the first electrodes 322a and the second electrodes 322c,
respectively. The control voltages of the same or opposite polarities may
be applied to the optical systems 322b, the first electrodes 322a and the
second electrodes 322c.

[0055]To increase luminance, the controller 321 applies control voltages
of the same polarity to the optical system 322b and the second electrode
322c, and applies a control voltage of the polarity, which is opposite to
that of the control voltage of the optical system 322b, to the first
electrode 322a, so that the optical system 322b can be moved closer to
the bottom of the light guide plate 310 by electrostatic force.

[0056]In contrast, to decrease luminance, the controller 321 applies
control voltages of the same polarity to the optical system 322b and the
first electrode 322a, and applies a control voltage of the polarity,
which is opposite to that of the control voltage of the optical system
322b, to the second electrode 322c, so that the optical system 322b can
be spaced farther apart from the bottom of the light guide plate 310 by
the electrostatic force generated by the electrically charged optical
system 322b and first electrode 322a.

[0057]Furthermore, the first electrode 322a may be made to be small enough
to minimize optical inference, and may be formed of an optically
transparent material.

[0058]The edge type backlight units 200 and 300, according to the present
invention, may further include optical members 230 and 330 respectively.
The optical members 230 and 330 serve to concentrate light so that light
being incident onto the light guide plates 210 and 310 from the light
sources `1` is directed to a preset direction, respectively.

[0059]The optical members 230 and 330 may each be constructed as a prism
or lens.

[0060]FIG. 4 is a view illustrating local dimming of an edge type
backlight unit according to the present invention.

[0061]It can be seen from FIG. 4 that the edge type backlight unit
performs local dimming by controlling the distance between an optical
system and a light guide plate.

[0062]In the case of an image signal which is predominantly dark with a
predetermined bright portion, all the light in the light guide plate,
except for the light lost by total reflection, is emitted in an upward
direction of the light guide plate only by an optical system drawn near
to the light guide plate. The quantity of light being emitted becomes
excessive without controlling the quantity of incident light, resulting
in excessively high luminance. Therefore, light sources `1` control the
quantity of incident light in association with the luminance control of
the luminance control unit. Thus, the power consumption of the backlight
unit can be reduced, since not many images require the maximum luminance
at the entire liquid crystal panel.

[0063]Also, the optical member directs light to a specific direction so
that the quantity of light can be controlled locally, and thus power use
can be further reduced.

[0064]As set forth above, according to exemplary embodiments of the
invention, the edge type backlight unit having smaller volume than the
direct type backlight unit can perform local dimming by controlling the
distance between the light guide plate and a plurality of optical systems
disposed under the light guide plate.

[0065]While the present invention has been shown and described in
connection with the exemplary embodiments, it will be apparent to those
skilled in the art that modifications and variations can be made without
departing from the spirit and scope of the invention as defined by the
appended claims.